A New Proactive Scheduling Methodology for Front-end Crude Oil and Refinery Operations under Uncertainty of Shipping Delay

The petroleum industry plays an important role in the economic development of the country. Advanced decision-supporting techniques such as planning and scheduling are needed to cope with challenges in crude oil supply chain management. Which have been studied and practiced for a long time, especially in the last two decades driven by increasingly intensive global competitions, more volatile feedstock and product markets, as well as stricter environmental regulations. In reality, the crude scheduling activities are highly vulnerable to disruptions brought by various uncertainties. For example, the shipping delay of crude vessels may disrupt the associated activities and cause the originally well-set schedule operations to become suboptimal or even infeasible.

In this research, a new large-scale continuous-time scheduling model has been developed for crude unloading, transferring, and processing (CUTP) systems to simulate and optimize the front-end and refinery crude-oil operations simultaneously. The scope of the scheduling problem includes crude oil unloading from vessels to storage tanks at onshore berths, transfer of crude from these tanks to charging tanks, charging crude distillation units and further processing of crude inside the refinery, which includes crude distillation, cracking, coking, reforming, hydrotreating, product blending and component recovery. The general objective of the proposed CUTP model is to maximize the total production profit under uncertainty of shipping delay; meanwhile, operation and product specifications, inventory limits, and production demands have to be satisfied.

To efficiently solve this large-scale mixed integer nonlinear programming problem without compromising problem complexity, a general mixed-integer nonlinear global optimization solver, ANTIGONE, has been employed. The profit maximization and the production flexibility maximization are generally two contradictory aspects that should be well balanced. The efficacy of the proposed scheduling model has been demonstrated by industrial-scale case studies. This work has three major contributions: (i) Simultaneous scheduling of front-end crude transfer and refinery processing with shipping delay uncertainty has been achieved. (ii) The shipping delay uncertainty has been taken into account to avoid refinery shut-down events by introducing an inventory-related time flexibility index. (iii) The relationship between the total profit and the minimum flexibility threshold is also given for a plant to manage its operational risks. It greatly increases the potential profitability and production flexibility of refineries.